An electromagnetic prospecting instrument for subsurface conducting zones     

Dharmajit G. Sarma  Sakti K. Biswas 《Pure and Applied Geophysics》1965,62(1):124-128

Summary A portable electromagnetic prospecting unit comprising a transmitter, receiver and resolver, designed and constructed to operate with a vertical setup of coils at a single frequency of 1250 cps, measures the components of the magnetic field at the receiver station resolved in phase and at quadrature with field near the transmitter. This may be used to locate vertical or steeply dipping conductors down to a depth of about 0.6 times the maximum workable transmitter receiver separation of 120 meters, the accuracy of measurements of the resolved components being better than 2%. The variation of resolved components over a buried conductor indicates its position and depth.This paper is published by the kind permission of the Director General, Geological Survey of India.  相似文献   

Leachate Mound Changes in Landfills Due to Changes in Percolation by a Cap     

Issa S. Oweis  Gopal C. Biswas 《Ground water》1993,31(4):664-674

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Implications of north pacific plate tectonics in central Alaska: Focal mechanisms of earthquakes     

B. Bhattacharya  N. N. Biswas 《Tectonophysics》1979,53(1-2)

The focal mechanisms for 86 selected earthquakes (3.0 m_b 5.5) located in central Alaska have been investigated from P-wave first motions; the data were gathered by local seismic networks. The results show a depth-dependent characteristic to the fault-plane solutions. For earthquakes having focal depths shallower than 60–70 km, the focal mechanisms indicate either strike-slip or normal faults, while for earthquakes with foci at intermediate depths the focal mechanisms correspond to thrust faults. The nature of the seismicity indicates the hinge line of the Pacific lithospheric plate under the study area to be striking N17°E from Cook Inlet towards interior Alaska. The comparison of the focal mechanisms with the seismicity shows that the strike-slip and normal faults are the predominant processes of stress release along the shallow section of the plate. The earthquakes with intermediate foci systematically occur along the inclined section of the plate. If the gently dipping nodal planes for these earthquakes are chosen as the fault planes, the focal mechanisms correspond to underthrust motions at the foci. In these, the slip vectors are oriented either to the west or north with the resultant being in the N30°W direction. The tension axes for the underthrust solutions are also found to be parallel to the local dip of the plate, indicating that the subducted plate in interior Alaska is undergoing gravitational sinking.  相似文献   

On the propagation of love waves in a heterogeneous layer lying on a homogeneous medium     

Arabinda Biswas 《Pure and Applied Geophysics》1966,64(1):5-8

Summary The present note is devoted to find out the possibility of propagation of love waves in a heterogeneous layer of finite depth lying on a homogenous semi-infinite elastic medium, the rigidity and density in the upper layer varying as (1–sinz), where is a constant andz is the vertical distance from the interface. The numerical results for the phase velocity for some special Earth models are given.  相似文献   

Earth-flattening procedure for the propagation of Rayleigh wave   总被引：1，自引：0，他引：1  

N. N. Biswas 《Pure and Applied Geophysics》1972,96(1):61-74

Summary The propagation of Rayleigh waves in the earth is investigated in the period range of about 60 to 590 seconds. It has been shown that a set of earth-flattening approximations can be used to transform the heterogeneous spherical earth into plane-layered earth on which the dispersion computations by matrix method can be applied effectively to describe the fundamental mode of spheroidal oscillations involving the crust and the mantly only.  相似文献   

Transmission of elastic waves through a second-order fluid layer sandwiched between elastic media     

Arabinda Biswas  S. B. Sinha 《Pure and Applied Geophysics》1970,78(1):42-47

Summary The present paper is concerned with the transmission of elastic waves through a second-order fluid layer sandwiched between homogeneous elastic media having identical properties. It is concluded that the transmission ratio increases with the increasing absolute values of visco-elastic co-efficient and also with the wavelength of the wave transmitted.  相似文献   

Dispersion-flocculation studies on hematite-clay systems     

B. Gururaj  J.P. Sharma  A. Baldawa  S.C.D. Arora  N. Prasad  A.K. Biswas 《International Journal of Mineral Processing》1983,11(4):285-302

Studies have been made on the separability of clay minerals such as kaolinite, illite and montmorillonite from hematite in dispersant-starch flocculant systems. The grossly different dispersibility of hematite from that of clay minerals aided separation by selective dispersion and flocculation. Moderate success has been achieved with a selectivity index nearing 4.0 (average recovery values around 80%).The studies have been extended to hematite recovery and clay rejection from the slimes of the Barsua iron ore washing plant owned by Rourkela Steel Plant, India. Limited success achieved in the starch selective flocculation method has been attributed to the difficulties associated with fine grain size, clay mineraloty and liberation.The ore exhibits the phenomenon of differential grinding. Hematite-rich coarser particles in the slime can be separated by differential settling in dispersant systems followed by selective flocculation in low-starch systems.  相似文献   

Frequency dependent characteristics of coda wave quality factor in central and southcentral Alaska     

G. J. Steensma  N. N. Biswas 《Pure and Applied Geophysics》1988,128(1-2):295-307

Coda wave quality factor (Q _c ) was investigated by using digital data (100 sample sec^–1) recorded by a vertical component short-period station installed for this study. The station was located in the greater Fairbanks area in central Alaska. From several hundred earthquakes recorded by this station in about a year, 27 earthquakes were selected for the above study; 7 of these selected earthquakes were located along the Alaska Wadati-Benioff zone (Pacific plate). The other 20 earthquakes were located in the area of intraplate seismicity (North American plate). The data was filtered using 9 pass-bands with center frequency varying from 1.5 Hz to 16 Hz with octave bandwidth. The values ofQ _c obtained from the coda amplitude decay rates measured on the filtered data after corrections due to the recording instrument and source-receiver separation show appreciable frequency dependence. The value ofQ _c varies in the range of 253 and 1190 corresponding to the frequency interval from 1.5 Hz to 16 Hz for the study area. This variation is close to that reported by others for the Kanto region of Japan. Moreover, the characteristics ofQ _c obtained in the present case seem to be independent of epicentral distance and hypocentral depth.  相似文献   

Solar cosmic ray composition above 10 MeV/nucleon and its energy dependence in the 4 August 1972 event     

Bertsch  D. L.  Biswas  S.  Reames  D. V. 《Solar physics》1974,39(2):479-491

Observations of the proton, helium, (C, N, O) and Fe-group nuclei fluxes made during the large 4 August 1972 solar particle event are presented. The results show a small, but significant variation of the composition of multiply-charged nuclei as a function of energy in the energy region above 10 MeV nucleon^–1. In particular, the He/(C, N, O) abundance ratio varies by a factor 2 between 10 and 50 MeV nucleon^–1 and the Fe-group/(C, N, O) ratio suggests a similar variation. Abundance ratios from the 4 August 1972 event are compared as a function of energy with ratios measured in other solar events to show that several of the earlier results are consistent with an energy variation like that observed in August 1972, while certain other events must have had a substantially different dependence of composition on energy. At energies 50 MeV nucleon^–1, the He/(C, N, O) abundance ratio for August 1972 is consistent with all earlier measurements made above that energy which suggests that variations may vanish at high energies.NASA/NAS Senior Resident Research Associate, on leave from TATA Institute of Fundamental Research, Bombay.  相似文献   

Signature of a paleogene submarine-fan from the Jenam Formation,Barail Group,Assam-Arakan orogen,northeastern India     

Ananya Biswas  Bhabani Prasad Mukhopadhyay 《Journal of the Geological Society of India》2011,78(6):510-522

Geological domains in northeastern India evolved though time after the rupture of the Gondwanaland. Collision of the Indian and the Burmese plates took place during the middle part of Cretaceous. Evolution of the Paleogene Barail trough, Neogene Surma and Tipam Groups took place gradually. The Barail trough originated at the active margin of the Indo-Burmese plate convergence. Previously, the Barail sedimentary wedge was interpreted to have been deposited in a deltaic to shallow-marine environment. Latter studies have proposed a new depositional model. The Barail Group, a part of the Assam-Arakan Orogen comprises the lowermost Laisong Formation, middle Jenam and upper Rinji Formation. Most of the Paleogene strata of the Barail Group carry imprints of a deep-water submarine fan near an active subduction zone. A deep-water proximal- to mid-fan depositional setting has been ascribed to the lower Laisong strata. Facies analysis of the extensive exposures of the Jenam Formation, near the Jenamghat, Assam, have enabled a detailed reconstruction of a proximal to mid-part of a submarine fan under an overall influence of turbidity currents and debris flow, ultimately evolving into turbidity currents. The Jenam sedimentary wedge bears tell-tale preservation of olistostromes (chaotic facies) with abundant volcaniclastics and basic rock fragments, massive sandstones, conglomeratic sandstone to sandstone-siltstone-shale and sandstone-siltstone-mudstones with profuse turbidites. Facies attributes amply signal the inherent instability of the Barail trough owing to its location near an active subduction zone. The Jenam suite of rocks containing a strong impress of volcanogenic materials along with quartzo-feldspathic rocks were mixed up by turbidity currents and shed into the submarine environment as the Jenam deep-water turbidites.  相似文献